The present invention relates to methods and apparatus for bending pipe and more particularly concerns bending of pipe as the pipe itself is being formed or withdrawn from a substantially continuous supply.
Sections of tubing or pipe having one or more bends formed therein, are widely used for a variety of applications of which an important application is use as automobile engine exhaust system pipe. At present, in the manufacture of automobile exhaust pipes, straight pipe sections of predetermined lengths are bent in manual or automatic bending machines, such as machines described in U.S. Pat. No. 3,974,676 for Tube Bending Machine and Carriage Therefor and U.S. Pat. No. 3,949,582 for Positioning Servo and Controlled Mechanism. Even where a semi-automatic loader is employed to load the pipe on the machine, the pipe sections are of pre-selected length and are removed by hand from a stack of such lengths. Welded pipe must be oriented by hand so that its seam has a predetermined orientation. This is required to ensure repeatability of bend dimensions, since position of the weld seam has a significant effect upon bend parameters.
Upon each loading of a pipe section in the machine, an end of the pipe is grasped by a collet. If the end is deformed in any manner, as from prior handling or the like, difficulties and time-consuming efforts are encountered in grasping of the pipe end by the collet. These aspects of pipe bending, among others, require the operator to be located close to the machine, which increases risks to personal safety.
Pipe sections are stored in pallets, hoppers, and racks, and forklifts and operators are now required for access to such storage. In addition, large areas of manufacturing facilities, sometimes in the order of three-quarters of total plant area, are employed for material storage in some operations.
Generally pipe is formed in separate facilities embodying large and expensive installations and requiring several people for operation. These are often set up to efficiently make a relatively long run of pipe of a single diameter and gage before a different pipe may be made. Change over for manufacture of pipe of a different diameter may take several hours.
The manufactured pipe is cut and often re-cut, then stored either at the pipe forming facility or at the pipe bending facility, or at both facilities, for two to three weeks or even longer periods. Stored pipe is coated with a protective coating such as oil or the like and, during storage, this coating will evaporate to an extent that depends upon the length of storage time and the environment of the storage area. This variable evaporation gives rise to significant bending errors since pipes with less oil coating will draw more, wrinkle less and have less springback than pipes with more oil coating. In other words, the precision or the actual dimensions of bend parameters of the pipe depend to a significant extent upon the length of time the pipe has been stored and the place in which it has been stored. Exactly the same bending techniques applied to two different pipe sections that have been stored for different times or in different places may result in different bend parameters of the finished bend pipe even though such two pipe sections were derived from the same run of formed pipe.
Thus it will be seen that a considerable amount of wasted effort, facilities, time and personnel, are involved in the system followed by most bent pipe manufacturers and further, the system has many disadvantages and inherent errors that significantly diminish precision and tolerance of bend parameters.
Accordingly, it is an object of the present invention to provide methods and apparatus for manufacturing bent pipe which avoid or minimize above-mentioned problems.